Motor-driven systems are generally used in the prior art, which systems depress the conventional spray head of the aerosol can. Said motor-driven systems, together with the further circuitry and the aerosol can, are housed in a casing. The batteries for supplying the power for the control and drive of the motor are likewise located in said casing. In some embodiments the aim is to make the life of the batteries equal to the life of the aerosol can or to make the battery life twice that of the aerosol can.
In U.S. Pat. No. 3,666,144 an attachment is described which is to be placed between the atomiser nozzle of an aerosol can and the aerosol can itself. A coil-operated valve is contained in said attachment. With this embodiment the life of the batteries can be extended appreciably because current consumption is appreciably limited.
In practice this type of simultaneous use of the aerosol can and the batteries proves particularly difficult to realise. This means that either the aerosol can is not emptied completely or that the battery is not exhausted at the time the aerosol can is changed. Moreover, it is necessary for maintenance staff to replace both the aerosol can and the batteries.
Some embodiments have indicators to display the number of times aerosol has been dispensed by the aerosol can or the residual power in the battery. This counting is ineffective if the aerosol can contains a greater or lesser number of doses. One problem with the battery indicator is that as soon as the battery is virtually empty no further indication can be given of the contents of the aerosol can or the contents of the batteries themselves. That is to say, there is no clear indication for maintenance staff. A positive approach to this problem, that is to say allowing an indicator to remain permanently lit if the battery is not yet empty, is found to consume a particularly high proportion of the battery charge and this approach is therefore also not desirable.
A further problem is that, especially in public toilets, a separate circuit is needed to prevent a dosage also being dispensed during the night when the toilets are not in use. For this purpose it is necessary to set the time or to use a day/night sensor, which is complex and the reason why, in practice, devices of this type continue to run day and night, which leads to wastage of the both the contents of the aerosol cans and of the batteries.